Dad and Brother's Girlfriend Are Caught in Couch Clinch

DEAR ABBY: My brother and his girlfriend, "Serena," moved in with my parents three years ago. They have since had a child who is almost 2. My brother did some things he shouldn't have, and now he's in prison. (He has eight months left to serve.) Serena doesn't work and barely takes care of their son. My parents seem to always have the little boy.

Last night, I dropped by the house unexpectedly. Mom was in bed, but I found my dad and Serena making out on the couch. I was furious. I could have killed her right there for doing that to my mom and my brother. Somehow I managed to keep my cool, but not before letting my presence be known.

Dad tried to act like what I saw was a game and wasn't real. I know what I saw, and I feel terrible. I don't know how to handle this. Should I tell my brother and my mom? I can never go back into that house ever again. As long as Serena is there, I am a time bomb waiting to explode. I'm afraid of what I might do to her. Please help me! -- "TICKING" SISTER IN N. CAROLINA

DEAR "TICKING": I'll try. The first thing you must do is recognize that, as tempting as it is to blame this all on Serena, your father is an adult and responsible for his actions. He is as guilty as Serena is, and attacking her is not the solution.

Because having Serena living under the same roof has proved too tempting for your father to resist, give him two weeks to move her and the baby out, or you will tell your mother what you saw. (I wouldn't be surprised if she already has an inkling.) If Serena goes, say nothing. To tell your brother that the mother of his child has been cheating on him with his father while he's incarcerated, and unable to do anything about it, would be to no one's benefit, so I strongly advise against it.